Spermatozoa are highly sensitive to oxidative stress owing to a lack of antioxidant defences and a high proportion of polyunsaturated fatty acids within their plasma membrane. A key hallmark of oxidative stress is the production of highly reactive electrophilic aldehydes, generated as a consequence of lipid peroxidation. In this study we have assessed the impact of three such aldehydes, acrolein (ACR), 4-hydroxynonenal (4HNE) and malondialdehyde (MDA) displaying different levels of electrophilicity (ACR>4HNE>MDA), on equine spermatozoa, a cell type that generates substantial concentrations of reactive oxygen species (ROS) as a by-product of their normal metabolism. Our study revealed that all three aldehydes readily adducted to sperm surface proteins located predominantly within the post-acrosomal region of the head, proximal centriole and tail. The impact of such adduction was manifest in a significant dose- and time-dependent decrease in sperm motility. Indeed, sperm motility was completely lost after only 3 hours of exposure to both ACR and HNE (P<0.0001). In the case of the less reactive MDA, the decline in motility was less pronounced but still proved to be significant (P<0.01) after 24 hours of treatment. Similarly, both mitochondrial and cytosolic levels of ROS were also significantly elevated following 3 hours of treatment for ACR and 4HNE (P<0.0001). MDA treatment again required a longer time period (24 vs 3 hours), and higher doses, to promote significant (P<0.01) increases in intracellular ROS levels. Finally, lipid peroxidation was significantly elevated after 3 hours for 4HNE (P<0.0001) and 24 hours for ACR and MDA (P<0.01). Future work will focus on refining our analysis of the functional implications of reactive aldehydes and oxidative stress on stallion spermatozoa and determining whether this information can be exploited for the development of diagnostic markers of stallion fertility and/or novel contraceptive strategies to tackle the sensitive issue of feral horse control.